1. Field of the Invention
The present invention relates to an anti-skid control system for an electrically operated vehicle having an electric motor operating as a generator to provide a regenerative torque for braking and to recover the braking energy by charging a battery, and more particularly to an anti-skid control system for controlling the regenerative torque in braking operation of the vehicle to prevent the vehicle's wheels from being locked.
2. Description of the Prior Art
In general, an electrically operated vehicle is provided with a regenerative braking system, in which rotational energy of the vehicle's wheel is transformed into electric energy and recovered by charging the battery, so as to extend a travel distance of the vehicle. The electrically operated vehicle is also provided with an anti-skid braking system for controlling the braking force applied to the vehicle's wheels to prevent the wheels from being locked, as disclosed in Japanese Patent Laid-open Publication No. 48-2515, for example.
In that publication, there is disclosed a system in which a switch (either mechanical switch or semiconductor) is turned off to block electric current fed to a regenerative braking control circuit when the skidding condition of a wheel is detected, so that the regenerative braking torque applied to the wheel is released to thereby prevent the wheel from skidding. Then, when the speed or acceleration of the wheel is increased to reach a certain value, the aforementioned switch is turned on to apply the regenerative braking torque to the wheel. In the case where the skidding condition of the wheel is detected again, the switch is turned off to release the regenerative braking torque applied to the wheel. With these operations repeated, the wheel is prevented from skidding.
In the above-described system, however, application of the regenerative braking torque to the wheel is intermitted in accordance with the on-off operation of the switch to thereby control the braking force applied to the wheel. That is, the regenerative braking torque is applied to the wheel immediately after the switch is turned on, whereas no regenerative braking torque is applied when the switch is turned off. Therefore, the magnitude of the braking force applied to the wheel is largely varied by intermitting the application of the regenerative braking torque to the wheel, so that it is difficult to stop the vehicle smoothly in case of the anti-skid operation.